Describe the search precisely
Record the sources searched, their coverage, the query, date interpretation and access permissions. Identify which fields and attachment contents were searchable. A question about a bank account number may require examination of attachments as well as the message body. Search logic must reflect how the data was represented.
Investigate the blind spots
Partially indexed or encrypted items, excluded folders, incomplete caches and lost historical sources can prevent a match. A migration or export may also change field representation. Review errors and collection reports and consider alternative spellings, aliases, character encodings and dates where justified. Avoid silently broadening the scope beyond the agreed authority.
Use bounded language
An appropriate result can say that no responsive message was identified in specified material using documented methods. It should distinguish that finding from a claim of non-existence. Conversely, do not speculate indefinitely that every absence conceals missing evidence. Explain the material limitations, the additional sources that could reasonably be tested and whether further work is proportionate. This gives the decision-maker a result that can be assessed and reproduced.
Sources & further reading
Primary references support the technical explanation. They do not establish D3 validation of a particular method.